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Immune Cells Regrow a Rat's Spinal Cord

Scientists have got a rat's severed spinal cord to regrow after injecting it with certain immune cells. The results, reported in the July Nature Medicine, have sparked hope that the technique might help repair brain and spinal cord injuries in people as well.

In mammals, peripheral nerves can often repair themselves, but damage to the brain and spinal cord is mostly permanent. Many researchers have tried to coax these crucial tissues into healing themselves by treating them with growth factors or nerve helper cells that are thought to secrete restorative chemicals. These techniques have worked in rats, but have not been successfully transferred to humans.

Michal Schwartz and her colleagues at the Weizmann Institute of Science in Rehovot, Israel, decided to pursue what appeared to be a clue to regeneration: Neurons that can repair themselves attract immune cells called macrophages to the site of injury, while nonrepairing cells suffer silently. Following up on this observation, Schwartz's group severed the spinal cords of 22 rats, which paralyzed their hind legs, then injected macrophages into the area surrounding the injury. The researchers monitored the rats' recovery over the next 19 weeks by recording their ability to move their hind legs. Rats that didn't receive macrophages regained only the slightest twitch to their legs, while most macrophage-treated rats could move their legs in a sweeping motion and occasionally use them to support some of their weight. "It's a partial but very dramatic recovery," Schwartz says. Her team also found that new nerve fibers had grown across the injury gap.

"It's a very provocative finding," says Dalton Dietrich, a neuroscientist at the University of Miami School of Medicine in Florida. He notes that scientists used to think that macrophages at a wound site might help damaged tissue because they contribute to inflammation. "But this suggests that macrophages may be releasing substances that promote regeneration," he says. He cautions that many other potential treatments for spinal cord injuries have shown similar promise early on, but failed to pan out in further animal tests.